This invention relates to security documents such as passport, bonds, banknotes, and security devices such as security passes and the like.
The security industry is always looking for new manufacturing techniques, materials and effects which offer improved and or additional security and which will offer the xe2x80x9cman on the streetxe2x80x9d greater assurance when exchanging such documents while also offering an aesthetically appealing document that people will look at.
Printed matter always has the problem of being copied or simulated by photocopying or scanning devices as well as simple printing techniques widely available in the commercial world. Therefore, devices that change colour or shape under various lighting conditions and or geometry make the task of counterfeiting or simulating the document much more difficult.
The introduction of the polymer security substrate has offered the perfect medium to produce secure devices in a cost effective and secure manner. As most high level security documents are already printed via the intaglio process, a well known method of printing which uses elevated temperatures and high pressures, 70xc2x0-90xc2x0 C. at 25-30 Mpa, the machines and special inks for this process are only sold to bona fide security printers, which offers a degree of inherent security.
In our International Patent Application PCT/AU98/00046, we describe a printed security document or device including a reflective or brightly coloured base layer and a raised printed image applied to that layer by a printing process, at least part of the raised printed image having a height of at least 5 xcexcm, the image being enhanced by the reflective or brightly coloured layer when viewed at different angles under different lighting conditions. Subsequent research on the effect created by this arrangement has revealed that it is important for best results for the base layer to be highly reflective and for the raised printed image to be printed in an ink having predetermined chroma and lightness.
The invention provides a security document or other device including a substrate, a smooth highly reflective layer applied to said substrate and having a reflectivity of at least 60 gloss units, and a raised printed image applied to said reflective layer by a printing process, at least part of said raised printed image having a height of at least 10 xcexcm, said printed image being printed using ink of a hue having a chroma value of at least 30 chroma units and/or a lightness of at least 50 lightness units.
By producing the printed image on a highly reflective layer as defined above, the raised printed image is significantly enhanced when viewed at different angles and under different lighting conditions and is therefore able to produce in the document or device a security effect which is readily noticeable to the naked eye, will maintain its effectiveness for the life of the document and will satisfy the anti copy requirements of security documents such as banknotes.
The invention also provides a method of producing a security document or other device, including the steps of applying a smooth highly reflective layer to a substrate, said reflective layer having a reflectivity of at least 60 gloss units, and printing a raised printed image on the reflective layer, at least part of said raised printed having a height of at least 10 xcexcm and being printed using ink of a hue having a chroma value of at least 30 chroma units and/or lightness of at least 50 L degrees (lightness units).
The smooth highly reflective layer can be applied by printing as part of the gravure printing process used to print security documents and devices, such as banknotes. If desired, other printing processes, such as silk screen printing, may be used to apply the layer. Alternatively, a substrate having the required reflectivity can be achieved by hot stamping of foil having the required reflectivity to the substrate.
Where the smooth highly reflective layer is applied by a printing process, it is applied in a manner which achieves a layer thickness of about 3 xcexcm.
The layer is preferably restricted to a relatively small region or patch of the substrate defining the security document or other device to thereby define a specific security feature in the document or device.
The substrate is preferably a smooth substrate such as a laminated polymer material of the type used in the production of Australian banknotes, and manufactured and sold by the applicant under the trade mark GUARDIAN, or any other smooth surfaced polymer suitable for use in the production of security documents or devices. Although paper substrates are not as smooth as polymer substrates, acceptable results can be achieved by printing or laminating a reflective patch onto a paper substrate, which is then calendared by the subsequent intaglio printing process.
Where the smooth highly reflective layer is applied by printing, the ink used should incorporate selected pigments and binders which will enable the cured reflective surface to withstand chemical and physical attack over an extended period of time, comparable to the expected life of the document.
The printed image is preferably applied by intaglio printing, or although other known printing processes capable of producing raised lines or dots on the reflective layer may be used. The printed image will typically have an average height of about 10 xcexcm to 100 xcexcm, which is about the upper limit of the height which can be achieved using the intaglio printing process, a similar width, and a spacing or pitch between adjacent lines or dots should be in a ratio height to pitch of about 1:1 to 1:3. In a practical example, the lines/dots in the image will have a height of about of 20 to 30 xcexcm, a similar width, and a pitch of about 30 xcexcm.
The adoption of the ratio outlined above results in the reflective patch remaining reflective in nature when viewed with a light source from behind, and the patch will dominate the perception of the viewer""s eyes. In addition, at lower viewing angles, there will still be enough of the surface of the patch in a non-reflective mode relative to the observer and the light source to give contrast to the relatively bright and reflective intaglio ink.
The intaglio ink used for printing the image should have a hue chroma value tending towards saturation: 60 chroma units. While the minimum chroma value should be about 30 chroma units, a practical chroma value to achieve best results will be at least 50 chroma units, which is relatively close to saturation. The lightness of the ink should similarly be greater than 50 L degrees, and the lightness will typically be of the order of 70 to 100 L degrees.
An appropriate lightness value can be achieved in an ink having the required hue and chroma values by the addition of a lightening agent such as TiO2 to the ink. The amount of TiO2 added to the ink will depend on the hue of the ink which is selected, and may vary from about 3% to about 10%.
The effects described above and below can be achieved to a certain extent by using pure colours in the intaglio inks, preferably hues located in the L*a*b* colour space quadrant as defined by Commission Internationale de I""Eclairage in 1976. However, for best results, the TiO2 addition described above improves the opacity of the printed image sufficiently to hide the reflective patch and provides additional reflectance so as to be readily observable when the metallic reflective patch is viewed beyond the 40 degree window illustrated in FIG. 4. The addition of titanium dioxide, in the preferred embodiment to 4% at the expense of the filler calcium carbonate, the above criteria of opacity and reflective specifications are achieved without losing any lightness or hue saturation. The increased reflectance of such enhanced intaglio inks allow the intaglio image to be clearly observable at an angle other than the viewing window of the reflective patch.